erl_scan

The Erlang Token Scanner

This module contains functions for tokenizing characters into
Erlang tokens.

Functions

string/1

string/2

string/3

Takes the list of characters String and tries to
scan (tokenize) them. Returns {ok, Tokens,
EndLocation},
where Tokens are the Erlang tokens from
String. EndLocation
is the first location after the last token.

{error, ErrorInfo, ErrorLocation}
is returned if an error occurs.
ErrorLocation is the first location after
the erroneous token.

string(String) is equivalent to
string(String, 1), and
string(String,
StartLocation) is equivalent to
string(String,
StartLocation, []).

StartLocation indicates the initial location
when scanning starts. If StartLocation is a line
attributes() as well as EndLocation and
ErrorLocation will be lines. If
StartLocation is a pair of a line and a column
attributes() takes the form of an opaque compound
data type, and EndLocation and
ErrorLocation
will be pairs of a line and a column. The token
attributes contain information about the column and the
line where the token begins, as well as the text of the
token (if the text option is given), all of which can
be accessed by calling token_info/1,2 or attributes_info/1,2.

A token is a tuple containing information about
syntactic category, the token attributes, and the actual
terminal symbol. For punctuation characters (e.g. ;,
|) and reserved words, the category and the symbol
coincide, and the token is represented by a two-tuple.
Three-tuples have one of the following forms: {atom,
Info, atom()},
{char, Info, integer()}, {comment, Info,
string()}, {float, Info, float()}, {integer,
Info, integer()}, {var, Info, atom()},
and {white_space, Info, string()}.

The valid options are:

{reserved_word_fun, reserved_word_fun()}

A callback function that is called when the scanner
has found an unquoted atom. If the function returns
true, the unquoted atom itself will be the category
of the token; if the function returns false,
atom will be the category of the unquoted atom.

return_comments

Return comment tokens.

return_white_spaces

Return white space tokens. By convention, if there is
a newline character, it is always the first character of the
text (there cannot be more than one newline in a white space
token).

return

Short for [return_comments, return_white_spaces].

text

Include the token's text in the token attributes. The
text is the part of the input corresponding to the token.

tokens/3

tokens/4

An opaque continuation

This is the re-entrant scanner which scans characters until
a dot ('.' followed by a white space) or
eof has been reached. It returns:

{done, Result, LeftOverChars}

This return indicates that there is sufficient input
data to get a result. Result is:

{ok, Tokens, EndLocation}

The scanning was successful. Tokens
is the list of tokens including dot.

{eof, EndLocation}

End of file was encountered before any more tokens.

{error, ErrorInfo, EndLocation}

An error occurred. LeftOverChars
is the remaining characters of the input data,
starting from EndLocation.

{more, Continuation1}

More data is required for building a term.
Continuation1 must be passed in a new call to
tokens/3,4 when more data is available.

The CharSpeceof signals end of file.
LeftOverChars will then take the value eof
as well.

reserved_word/1

token_info/1

Returns a list containing information about the token
Token. The order of the
TokenInfoTuples is not
defined. See token_info/2 for
information about specific
TokenInfoTuples.

Note that if token_info(Token, TokenItem) returns
undefined for some TokenItem, the
item is not included in TokenInfo.

Returns a list containing information about the token
Token. If one single
TokenItem is given the returned value is
the corresponding
TokenInfoTuple, or undefined if the
TokenItem has no value. If a list of
TokenItems is given the result is a list of
TokenInfoTuple. The
TokenInfoTuples will
appear with the corresponding TokenItems in
the same order as the TokenItems
appear in the list of TokenItems.
TokenItems with no value are not included
in the list of TokenInfoTuple.

The following TokenInfoTuples with corresponding
TokenItems are valid:

attributes_info/1

Returns a list containing information about the token
attributes Attributes. The order of the
AttributeInfoTuples is not defined.
See attributes_info/2 for
information about specific
AttributeInfoTuples.

Note that if attributes_info(Token, AttributeItem)
returns undefined for some AttributeItem in
the list above, the item is not included in
AttributesInfo.

Returns a list containing information about the token
attributes Attributes. If one single
AttributeItem is given the returned value is the
corresponding AttributeInfoTuple,
or undefined if the AttributeItem
has no value. If a list of AttributeItem
is given the result is a list of
AttributeInfoTuple.
The AttributeInfoTuples
will appear with the corresponding AttributeItems
in the same order as the AttributeItems
appear in the list of AttributeItems.
AttributeItems with no
value are not included in the list of
AttributeInfoTuple.

The following AttributeInfoTuples with
corresponding AttributeItems are valid:

The line and column where the token begins, or
just the line if the column unknown.

{text, string()}

The token's text.

set_attribute/3

Sets the value of the line attribute of the token
attributes Attributes.

The SetAttributeFun is called with the value of
the line attribute, and is to return the new value of
the line attribute.

format_error/1

Takes an ErrorDescriptor and returns
a string which
describes the error or warning. This function is usually
called implicitly when processing an ErrorInfo
structure (see below).

Error Information

The ErrorInfo mentioned above is the standard
ErrorInfo structure which is returned from all IO
modules. It has the following format:

{ErrorLocation, Module, ErrorDescriptor}

A string which describes the error is obtained with the
following call:

Module:format_error(ErrorDescriptor)

Notes

The continuation of the first call to the re-entrant input
functions must be []. Refer to Armstrong, Virding and
Williams, 'Concurrent Programming in Erlang', Chapter 13, for a
complete description of how the re-entrant input scheme works.